1. Field of the invention
The present invention relates to a wire-wound common-mode choke coil used as a noise filter or other component for blocking common mode noise.
2. Description of the Related Art
In FIG. 8, a common-mode choke coil for blocking common-mode noise includes a first winding 22 connected between an input terminal electrode 1a and an output terminal electrode 2a, and a second winding 23 connected between an input terminal electrode 1b and an output terminal electrode 2b. The first winding 22 and the second winding 23 are bifilar-wound in the same direction on a core member 20 which is made of a magnetic material, such as a ferrite.
FIG. 9 is a bottom perspective view showing the core member 20 of a conventional common-mode choke coil, which includes a winding core 11 which is arranged to accommodate the windings 22 and 23 thereon, and includes square flanges 12 and 13 disposed at both ends of the winding core 11. Grooves 14 and 15 are formed in the flanges 12 and 13, respectively, and extend from a side of each flange toward the winding core 11. With the formation of the grooves 14 and 15, a pair of legs 12a and 12b and a pair of legs 13a and 13b are provided with the grooves 14 and 15, respectively, between each pair of legs, and the legs support the core member 20. Terminal electrodes 1a, 1b, 2a, and 2b are provided on the ends of the legs 12a, 12b, 13a, and 13b, respectively.
In FIG. 10 shows a conventional coil in which the first and second windings 22 and 23 are wound in a single layer on the winding core 11 of the core member 20. Ends 22a and 22b of the first winding 22 and ends 23a and 23b of the second winding 23 are electrically connected to the terminal electrodes 1a and 2a and the terminal electrodes 1b and 2b, respectively.
In the conventional wire-wound common-mode choke coil 10 in FIG. 10, a problem occurs in that the bottom edges of the grooves 14 and 15 formed in the flanges of the core member 20 are flush with the periphery of the winding core 11, and the vertical surfaces of the legs 12a, 12b, 13a, and 13b extend perpendicularly relative to the periphery of the winding core 11. Therefore, when a stress is applied to the legs 12a, 12b, 13a, and 13b during winding of the first and second windings 22 and 23 on the core member 20, the stress is concentrated to the lower parts of the legs 12a, 12b, 13a, and 13b, which extends from the periphery of the winding core 11, thereby breaking the legs 12a, 12b, 13a, or 13b. 
The following is a description of an inspection by image analysis of the first and second windings 22 and 23 in a wound-state, in the common-mode choke coil 10. The first and second windings 22 and 23 are visible between two legs of the core member 20, for example, the legs 13a and 13b. When the windings are viewed along arrow A in FIG. 10, it is possible to determine whether the windings 22 and 23 are properly wound on the winding core 11 by analyzing the image obtained.
In the image analysis, only one layer of windings, for example, a layer of the first winding 22, is visible through the groove 15 between the legs 13a and 13b of the core member 20, as shown in FIG. 11, when the first and second windings 22 and 23 are properly wound on the winding core 11, as shown in FIG. 10. On the other hand, overlapped windings 22 and 23 are identified through the groove 15 between the legs 13a and 13b, as shown in FIG. 13, when the first and second windings 22 and 23 are improperly wound, as shown in FIG. 12. Therefore, the wound-state of the first and second windings 22 and 23 is detected by analyzing the image of the first and second windings 22 and 23 visible through the groove 15, and thus, it is determined whether the first and second windings 22 and 23 are properly arranged.
However, a problem in a conventional wire-wound common-mode choke coil is that the result of the detection of the wound-state of the first and second windings 22 and 23 visible through the groove 15 varies according to the color and the diameter of the wire, the overlapping position, the overlapped state, or other factors and characteristics of the windings 22 and 23. Therefore, the inspection of the wound-state via image analysis is difficult and not reliable in a conventional wire-wound common-mode choke coil.
To overcome the problems described above, preferred embodiments of the present invention provide a wire-wound common-mode choke coil in which a core member is provided with a sufficient mechanical-strength and is constructed such that a reliable inspection of the wound state of windings on the core member can be performed.
According to one preferred embodiment of the present invention, a wirewound common-mode choke coil preferably includes a core member having a winding core, flanges disposed at both ends of the winding core, a plurality of legs located at both ends of grooves provided at the flanges, and terminal electrodes, each of the terminal electrodes being provided at the end of each of the legs and connected to ends of a plurality of windings wound on the winding core. At least four terminal electrodes are provided in the wire-wound common-mode choke coil. Bottom surfaces of the grooves are spaced from the periphery of the winding core, and protrusions are provided at ends of the winding core. The flank of the protrusions are preferably gradually elevated toward the flanges.
The protrusions are preferably provided at the lower portions of the legs and protrude out from the winding core, and also at the bottom surfaces of the grooves, thereby improving the mechanical strength of the legs and alleviating stress concentration to the lower portions of the legs, protruding out from the winding core.
The mechanical strength of the legs may be greater and the stress concentration may be alleviated by arranging protrusions which protrude out from the periphery of the winding core which extends toward the legs, higher than the bottom surface of the grooves, thereby increasing the cross-sectional areas of the protrusions.
The determination as to whether the windings are properly arranged may be performed simply by determining whether or not the windings are visible through one of the grooves. The bottom surface of the grooves is elevated from the periphery of the winding core by about 1.0 to about 1.5 times the diameter of the wire of the windings. The windings are not visible through a groove when the windings are properly wound, and the windings are visible through the groove when the windings are improperly wound.
Other features, elements and advantages of the present invention will become more apparent from the detailed description of preferred embodiments of the present invention below with reference to the attached drawings.